This brief scientific article relates our ability to perform physical acts without thought thus freeing our minds (reducing cognitive load) to simultaneously handle other urgent matters more efficiently.
In the defense world we tend to toss out "buzz words" without thought as to their actual meaning and context. "Stress Inoculation Training" is something often spoken about, but rarely examined for better benefit.
Automaticity in Sport provides fantastic insight as to why it's important to train properly and correctly perform elemental tasks thousands of times to become expert.
Additionally here is a PDF explaining proper methodology for task analysis. This can easily be applied to defensive skills, such as: drawing from holster, taking the shot, etc.